U.S. patent number 5,317,657 [Application Number 07/922,267] was granted by the patent office on 1994-05-31 for extrusion of polymer waveguides onto surfaces.
This patent grant is currently assigned to International Business Machines Corporation. Invention is credited to Antonio R. Gallo, James J. McDonough, Gordon J. Robbins, Robert R. Shaw.
United States Patent |
5,317,657 |
Gallo , et al. |
May 31, 1994 |
**Please see images for:
( Certificate of Correction ) ** |
Extrusion of polymer waveguides onto surfaces
Abstract
A waveguide structure is directly extruded onto a surface from a
nozzle placed a predetermined distance above the surface and which
is moved relative to the surface, preferably by means of a
translation table. The predetermined distance is preferably
maintained constant and the speed of relative motion regulated to
achieve a uniform degree of molecular orientation within the
extruded material, thus maintaining a sufficiently uniform
refractive index along the axis of the waveguide. Partitions within
the nozzle allow the formation of a layered waveguide or the
simultaneous formation of concentric cladding or protective layers.
The waveguides are advantageously formed as a curtain which is
later patterned, by direct writing on the surface or between chips
mounted on an electronic module.
Inventors: |
Gallo; Antonio R. (Pleasant
Valley, NY), McDonough; James J. (Fishkill, NY), Robbins;
Gordon J. (Wappingers Falls, NY), Shaw; Robert R.
(Poughkeepsie, NY) |
Assignee: |
International Business Machines
Corporation (Armonk, NY)
|
Family
ID: |
25446796 |
Appl.
No.: |
07/922,267 |
Filed: |
July 30, 1992 |
Current U.S.
Class: |
385/14;
156/244.11; 385/131; 385/142; 385/144; 385/145; 385/143; 385/132;
385/130; 264/1.7; 385/123; 264/1.1; 264/1.24; 65/401; 65/391;
264/1.36 |
Current CPC
Class: |
B29C
41/36 (20130101); B29D 11/00663 (20130101); G02B
6/132 (20130101); G02B 6/138 (20130101); B29C
48/022 (20190201); G02B 6/1221 (20130101); B29C
67/00 (20130101); B29C 48/03 (20190201) |
Current International
Class: |
B29C
41/34 (20060101); B29C 41/36 (20060101); B29C
47/00 (20060101); B29D 11/00 (20060101); G02B
6/138 (20060101); G02B 6/13 (20060101); G02B
6/122 (20060101); G02B 6/132 (20060101); B29C
67/00 (20060101); B29C 047/00 () |
Field of
Search: |
;156/244.11
;264/1.1,1.5,1.7 ;385/14,123,130,131,132,142,143,144,145 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
IBM Technical Disclosure Bulletin, vol. 33, No. 3A, Aug. 1990;
"Buried TI In-Diffused Waveguide on Lithium Niobate"; J. Ewen.
.
IBM Technical Disclosure Bulletin, vol. 33, No. 6B, Nov. 1990;
"Two-Level Chip Optical Waveguide"; J. M. Leas; pp. 34-38. .
IBM Technical Disclosure Bulletin, vol. 28, No. 1, Jun. 1985;
"Module Interconnection by Optical Fibers"; R. E. Stadler; pp.
237-238. .
IBM Technical Disclosure, vol. 33, No. 2, Jul. 1990; ". . . Silicon
Nitride Waveguide Fabrication"; pp. 156-157..
|
Primary Examiner: Weston; Caleb
Attorney, Agent or Firm: Whitham & Marhoefer
Claims
Having thus described my invention, what I claim as new and desire
to secure by Letters Patent is as follows:
1. A method of forming a waveguide on a surface, said method
including the steps of
positioning an extrusion nozzle a predetermined distance above said
surface,
forcing a viscous waveguide material through said extrusion
nozzle,
relatively moving said nozzle and said surface, and
maintaining a predetermined level of tension in said viscous
waveguide material between said nozzle and said surface.
2. A method as recited in claim 1, wherein said nozzle includes at
least one partition and said forcing step includes simultaneously
forcing viscous materials separated by said at least one partition
through said extrusion nozzle.
3. A method as recited in claim 1, including the further step of
patterning said extruded material.
4. A method as recited in claim 1, including the further step
of
performing a treatment operation on said surface.
5. A method as recited in claim 4, wherein said treatment operation
includes
applying a surfactant to said surface.
6. A method as recited in claim 4, wherein said treatment operation
includes
exposing said surface to a plasma.
7. A method as recited in claim 2, including the further step
of
performing a treatment operation on said surface.
8. A method as recited in claim 7, wherein said treatment operation
includes
applying a surfactant to said surface.
9. A method as recited in claim 7, wherein said treatment operation
includes
exposing said surface to a plasma.
10. A method as recited in claim 1, wherein said surface is the
surface of an electronic module.
11. A method as recited in claim 9, wherein said electronic module
has chips mounted thereon and said viscous material is deposited
between said chips.
12. A waveguide having all gradients of refractive index therein
oriented approximately along an optical axis of said waveguide
formed on a surface by a process including the steps of
positioning an extrusion nozzle a predetermined distance above said
surface,
forcing a viscous waveguide material through said extrusion
nozzle,
relatively moving said nozzle and said surface
maintaining a predetermined level of tension in said viscous
waveguide material between said nozzle and said surface.
13. A waveguide as recited in claim 12, wherein said nozzle
includes at least one partition and said forcing step includes
simultaneously forcing viscous materials separated by said at least
one partition through said extrusion nozzle.
14. A waveguide as recited in claim 12, including the further step
of patterning said extruded material.
15. A waveguide as recited in claim 12, including the further step
of
performing a treatment operation on said surface.
16. A waveguide as recited in claim 15, wherein said treatment
operation includes
applying a surfactant to said surface.
17. A waveguide as recited in claim 15, wherein said treatment
operation includes
exposing said surface to a plasma.
18. A waveguide as recited in claim 13, including the further step
of
performing a treatment operation on said surface.
19. A waveguide as recited in claim 18, wherein said treatment
operation includes
applying a surfactant to said surface.
20. A waveguide as recited in claim 18, wherein said treatment
operation includes
exposing said surface to a plasma.
21. A waveguide as recited in claim 13, wherein said waveguide
includes a plurality of layers formed by said forcing step.
22. A waveguide as recited in claim 13, wherein said waveguide
includes at least one layer concentrically formed around the
waveguide.
23. A waveguide as recited in claim 12, wherein said surface is the
surface of an electronic module.
24. A waveguide as recited in claim 23, wherein said electronic
module has chips mounted thereon and said viscous material is
deposited between said chips.
Description
DESCRIPTION
Background of the Invention
1. Field of the Invention
The present invention generally relates to the production of
optical waveguides and, more particularly, to the formation of
optical waveguides as a portion of another device, such as an
electronic module.
2. Description of the Prior Art
Optical communications have become increasingly popular in recent
years due to their large bandwidth and freedom from most forms of
electromagnetic interference. Telephone and local or wide area
digital communications networks are exemplary of such applications.
Optical communication links have also been used in individual
devices such as alarm systems where disturbance of the optical link
is detected. Further, in some high performance electronic
equipment, the high bandwidth and freedom from interference make
optical communication very desirable for communication or
distribution of clock and other high frequency digital signals.
The structure of electronic circuit modules such as multi-layer
modules of materials such as polymers or ceramics is also a
suitable application for optical communication. These multilayer
modules are capable of providing complex interconnection of a
plurality of separate chips, each of which can be formed in
accordance with mutually incompatible technologies and which may be
operated over differing voltage ranges such as for bipolar and CMOS
devices. The number of chips which may be accommodated is
essentially arbitrary and it is not uncommon for a plurality of
different clocks to be present on the same module. These clocks
must usually be synchronized and may require synchronizing or
master clock signals to be delivered at different voltages. If
electrical signals are used, voltage conversion must often be
provided which may, in turn, cause a significant delay of a
synchronizing signal pulse. Therefore, optical communication of
such signals is particularly desirable.
Past attempts to provide a waveguide on a surface or within a layer
of an electronic module have been less than fully successful since
such a layer is typically applied by a so-called spin process. As
an underlying surface of the device is rapidly rotated, a waveguide
material is applied to the surface at the axis of rotation. The
centrifugal forces due to the spinning causes a layer to be formed
with high uniformity of thickness. The spin process is well-known
and the process of choice for application of many diverse materials
to different surfaces and in numerous applications.
However, there are two principle drawbacks to the spin process for
forming a waveguide. First, the spin process does not generally
form a uniformly thick layer when the topology of the surface is
other than planar. Differences in thickness or curvature of the
surface of the layer may cause light loss or the pick-up of ambient
light. Second, and more importantly, the spin process may radially
stress the layer non-uniformly with distance from the axis of
rotation. This stress, which is largely dependent on the molecular
weight of the polymer, affects the alignment of molecules in the
waveguide and causes the waveguide layer to be anisotropic. That
is, a radial gradient of the refractive index over the distance
from the spin axis may result. It has also been reported that a
variation of the refractive index with angle about the spin axis
will also be produced. Further, the optical waveguide generally
must be patterned, and such patterning requires additional
processing steps. Without patterning, the intensity of the
communicated light (which may be outside the visual spectrum)
diminishes significantly with distance from the source even when
light losses can be kept low. On the other hand, the radial change
of refractive index causes a change in refractive index at an angle
to the axis of non-radial waveguides, causing increased light loss.
Further, the surfaces formed by patterning are usually sufficiently
irregular to scatter light and result in increased light loss.
Additionally, spin coating cannot readily be accomplished after
chips are in place on the module.
It is known to form optical fiber waveguides by extrusion and to
form cladding layers with differing refractive indices thereon by
coextrusion as taught is U.S. Pat. Nos. 4,806,289 and 4,871,487,
both issued to Laursen et al. However, the extrusion processes
disclosed therein include steps for drawing the fiber in tension to
establish a final cross-sectional size and uniformity of stress
applied to achieve desired molecular orientation to obtain a
uniform index of refraction along the optical fiber. This drawing
process is therefore not compatible with the formation of an
optical waveguide directly on a surface or to the solution of
radial molecular orientation and resulting radial gradients of
index of refraction due to application of optical waveguides to
surfaces by spin coating.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an
alternative to the formation of waveguides on surfaces by spin
processes.
It is another object of the invention to provide a generally linear
waveguide on a surface in a manner and of a structure which can
accommodate severe surface topology without substantial light loss
or signal interference.
It is a further object of the invention to provide any of a
plurality of waveguide structures on a surface by a substantially
common process involving only minor variations corresponding to
particular waveguide structures.
It is yet another object of the invention to provide a waveguide on
a surface of an electronic module which is compatible with other
processes which may be required in the fabrication of such a
module.
It is a yet further object of the invention to provide optical
communication in an electronic circuit module in a manner
consistent with the electronic and structural design thereof and
requiring no displacement of electrical structure.
In order to accomplish these and other objects, the invention, in
essence, provides for the direct extrusion of an optical waveguide
onto a desired surface. In the course of such extrusion, the radial
forces will inherently be substantially constant and the axial
forces can be sufficiently regulated to avoid significant changes
in refractive index along the waveguide. Further, an extruded
waveguide is inherently linear and will deliver light of
substantially undiminished intensity from a transmitter to a
receiver over the short distances involved in an electronic circuit
module. The extruded waveguide can be applied over conductors or a
passivation layer applied thereover and between pins of an
electronic module and thus, since such space is not otherwise
usable, such optical communication effectively requires no
"footprint" on the module. Further, the extrusion process is
applicable to a large number of materials which can be chosen to
avoid conflicts with other processes involved in the fabrication of
electronic modules.
In accordance which one aspect of the invention, a method of
forming a waveguide on a surface is provided including the steps of
positioning an extrusion nozzle a predetermined distance above a
surface, forcing a viscous material through the extrusion nozzle,
relatively moving the nozzle and the surface and maintaining a
predetermined level of tension in said viscous material between
said nozzle and said surface.
In accordance with another aspect of the invention, a waveguide
formed on a surface is provided by a process including the steps of
positioning an extrusion nozzle a predetermined distance above the
surface, forcing a viscous material through the extrusion nozzle,
relatively moving the nozzle and the surface, and maintaining a
predetermined level of tension in the viscous material between said
nozzle and said surface.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other objects, aspects and advantages will be
better understood from the following detailed description of a
preferred embodiment of the invention with reference to the
drawings, in which:
FIG. 1 is a schematic view of an apparatus for the extrusion on an
optical waveguide,
FIG. 2 is a simplified diagram of the top surface of an exemplary
electronic circuit module showing a preferred location of optical
waveguides,
FIG. 3 is a schematic diagram of a nozzle for extruding a waveguide
comprising one or more layers in accordance with one embodiment of
the invention,
FIG. 4 is a schematic diagram of a nozzle for simultaneously
extruding a waveguide and a concentric cladding therefor, and
FIGS. 5 and 6 illustrate different waveguide cross-sections which
can be obtained in accordance with the invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
Referring now to the drawings, and more particularly to FIG. 1,
there is schematically shown an exemplary apparatus 100 by which
the invention can be practiced. The basic arrangement of this
apparatus 100 is a mechanical arrangement by which relative motion
can be achieved between an extrusion nozzle 130 and the surface of
a substrate or layer 150. It is deemed preferable to achieve this
relative motion by means of a translation table which carries the
substrate or layer and is movable, for example, in orthogonal
directions at high precision and controllable speed under control
of a programmed computer in a manner well-understood in the art.
This arrangement is preferred in order to minimize vibration and
independent movement of the extrusion nozzle 130 in directions
parallel to the surface which could introduce irregularities in
molecular orientation of the extruded material.
The actual extrusion of the waveguide material 120 which is
preferably a polymer such as polyimide is controlled by a material
pump and reservoir 110 which also preferably includes structure
such as heaters or mixing apparatus for maintaining the condition
(e.g. viscosity, solvent content, etc.) of the waveguide material.
This extrusion apparatus may also include nozzle height sensor
structure 140, 145 in order to regulate tension in the extruded
material as it traverses topological features, if any, of the
surface upon which the waveguide is deposited. The nozzle height
transducer 145 could be of a mechanical, optical or other type and
is not critical to the practice of the invention as long as it can
resolve whatever topological features may exist on the surface 150.
The maintenance of an approximately constant predetermined
separation of the nozzle and the surface is important to the
practice of the invention since the unsupported length of extruded
viscous material is placed in viscous tension by gravity and the
relative movement of the nozzle and surface. This viscous tension
largely determines the finished transverse dimension of the
waveguide and also provides regulation of the degree of molecular
orientation in order to achieve a uniform refractive index along
the axis of the waveguide. Therefore it is important to the
practice of the invention to maintain a predetermined level of
viscous tension in the unsupported length of extruded material by
regulating nozzle height and writing speed. As a practical matter,
this is accomplished principally through the gap or separation
between the extrusion nozzle 130 and the surface 150. It should be
noted, however, that no molecular orientation by tension is
required in order to successfully practice the invention since the
orientation of refraction gradients engendered by spin coating are
avoided by direct writing. Preferably, however, the degree of
molecular orientation should be as constant as possible.
Chips 160 are shown as being attached to the surface 150 in FIG. 1
as is possible in some embodiments of the invention. In any event,
the space between chips 160 is not otherwise used and the extrusion
of waveguides at locations other than chip locations, as is more
particularly shown in FIG. 2, therefore, requires no additional
space of the substrate or layer surface. This feature of the
present invention also allows optical waveguides to be retrofit
onto existing modular circuit components and other devices. The
chips 160 are generally attached on the surface 150 in a matrix
pattern as shown in FIG. 2. Thus, the spaces between the chips
forms an orthogonal array of potential paths for the optical
waveguides 180 in order to communicate with clock chips 165
(indicated by a filled rectangle) which are typically centrally
located within associated regions of the surface 150. Further, if
desired, the optical waveguide can be brought out to the perimeter
of the module as shown at 190 to allow communication to or from
other modules either directly or through optical couplers and
additional optical links, the design of which may be in accordance
with that disclosed in "Module Interconnection by Optical Fibers",
IBM Technical Disclosure Bulletin Vol. 28, No. 1, June 1985, pp.
237-238. However, the design of the external optical link, if used,
is not critical to the practice of the invention.
Referring now to FIG. 3, one embodiment of the invention will now
be discussed. In this embodiment, a nozzle having a generally
linear footprint is used to extrude a pattern of waveguide of any
arbitrary width up to and including the entire width of the surface
150. In this latter case, the linear footprint of the nozzle would
extend along the entire length of dashed line 210 to extrude a
"curtain" 200 of waveguide. In such a case, the waveguide is
preferably patterned. The linear nozzle causes some stressing of
the waveguide material in a direction parallel to the linear nozzle
opening. However, since the patterning of the curtain waveguide
would preferably follow orthogonal paths and if the nozzle is
oriented along a direction of one of those orthogonal paths, the
angle of any gradient in the refractive index of the waveguide to
the axis of the waveguide is minimized and light loss can be kept
within usable limits.
Incidentally, the formation of waveguides as a "curtain" which is
thereafter patterned is the only circumstance which is necessarily
incompatible with the presence of chips 160 on the surface 150.
Although the desired routing of a waveguide may traverse a chip
location in some designs and which would necessitate removal of the
chip at such a location, if the waveguides are confined to
locations between chips, it is immaterial whether the chips are
present or not. It is also possible that the size or design of the
extrusion nozzle might require chips to be removed (or attached
after the formation of the waveguide) but the extrusion nozzles
which have been used to date are generally of cylindrical exterior
shape and of a diameter which only slightly exceeds the finished
diameter of the waveguide and thus can successfully extrude
waveguides with the chips in place.
Alternatively, the width W can be limited to any desired degree, in
which case patterning can be avoided. Also, change of index of
refraction across the width of the waveguide is reduced as the
width of the waveguide is reduced. Provision for turning the nozzle
to coincide with the orthogonal direction of relative motion
between the nozzle and the surface thus results in an extruded
waveguide of good uniformity and low light loss. Distribution
structures to split the input light may also be readily formed in
this way. In practice, it has been found that if contact can be
made between different extruded segments prior to the evaporation
of solvent from the segments, the segments will coalesce to form a
single waveguide. Alternatively, the drying of solvent from one
segment will allow one waveguide to be overlaid on or to cross
another.
Regardless of the waveguide width, one or more partitions, such as
240 may be advantageously formed within the nozzle so that a
plurality of layers 220, 230 with different refractive indices
(e.g. for cladding above and/or below the waveguide) or protective
properties (e.g. resistance to organic liquids and greases) can be
simultaneously formed. By formation of such a compound nozzle so
that one layer is slightly wider than an underlying layer, one or
more such cladding or protective layers may be made to enclose the
edges of the waveguide, as well.
In accordance with another embodiment of the invention, as shown in
FIG. 4, the extrusion nozzle 130' may be of circular (or
rectangular, as a variation of the nozzle of FIG. 3) shape and
partitions 240' may be provided concentrically therein, as shown in
cutaway cross-section. If materials of different refractive indices
are extruded through such a nozzle, a concentric cladding for the
entire periphery of the section of the waveguide is formed
simultaneously with the waveguide. Such a structure, having a lower
refractive index material cladding surrounding a higher refractive
index waveguide, is necessary if the waveguide is to operate in a
total internal reflection mode and particularly if the surface on
which the waveguide is to be deposited has a higher refractive
index than that of the chosen waveguide material. Alternatively or
additionally, a protective material can be extruded to surround the
waveguide of waveguide and cladding simply by providing additional
concentric partitions. Either cladding or protective material, if
opaque, can protect the waveguide from susceptibility to ambient
light.
It should also be noted that distribution structures such as
splitters and couplers can also be formed in the same manner as the
layered structure of FIG. 3. Alternatively, of course, separate
waveguides could be extruded from a single transmitter such as at
190 of FIG. 2 to each of a plurality of receivers such as clock
chips 165. In this regard, it should be noted that the nozzles and
waveguides can be made very small and a substantial number of such
waveguides can be placed in the gap between chips on a module at
typical spacings thereof. Specifically, diameters of the extrusion
nozzles are preferably in the range of 15-50 mils and the waveguide
may be reduced further by providing an increased writing speed
(e.g. movement of translation table 170) relative to the speed of
the extruded material through the nozzle as well as by the spacing,
h, preferably in the range of 3-5 mils, of the nozzle tip from the
surface 150, as shown in FIG. 4, as is also the case with the
thickness of the waveguide formed in accordance with FIG. 3. In
this regard, the final transverse dimensions of the waveguide will
also be affected by extrusion pressure and material viscosity.
The above techniques of extruding waveguides onto surfaces are
largely independent of the material of which the surface is
composed. Relatively severe topologies may be accommodated by
providing for sensing of surface height. Even if the surface is
relatively planar, it may be desirable to provide for such surface
height sensing in the event one waveguide is made to overlie or
cross another, as discussed above. The techniques according to the
invention are also applicable to a wide variety of waveguide,
cladding and protective materials such as polyacrylates,
polycarbonates, polystyrenes, polyimides and other polymers.
Virtually the only constraint on the material used is that for the
"curtain" form of waveguide of a width which requires patterning
and subsequent attachment of chips to the module, the cured
material must be able to withstand the temperatures involved in
soldering or otherwise attaching the chips.
Photosensitive polymers such as photosensitive polyimides also
provide the advantage of selective curing since such materials may
be caused to form cross-linkages and become cured by exposure to
light. This provides the advantage of being able to cure the
waveguide prior to other heat treatment steps or rapid curing
treatments such as microwave curing which may be necessary in
regard to the remainder of the module. Such differential curing may
also be advantageously used to control wall angle and profile of
the waveguide structure especially in such rapid curing processes
which might otherwise cause distortion of the waveguide.
As shown in FIGS. 5 and 6, the cross-sectional shape and wall angle
of the waveguide as well as the area of attachment to the surface
can be controlled to a substantial degree before curing by
treatment of the surface with surfactants or by other processes
such as reactive ion etching or plasma treatment. Depending on the
materials of the surface and the outer layer of the waveguide, the
surface will be wetted to a greater or lesser degree by the
extruded material. This wetting action will determine the wall
angle 300 where the waveguide is attached to the surface. The use
of surfactants, etching or plasma treatment generally causes an
increase in this wetting action and will cause the final
cross-section of the waveguide to resemble FIG. 6 more than that of
FIG. 5. The edges of the waveguide produced in accordance with the
embodiment of the invention illustrated in FIG. 3 can also be
adjusted in the same manner. In either case, the adjustment may
affect both the optical properties and the structure and adherence
of the waveguide to the surface or these effects may be separated
by the use of cladding 310 around the waveguide 320. It should also
be noted that the waveguide cross-section may be altered
independently of the wall angle at the base thereof by heat
treatment (e.g. above the glass transition temperature of the
waveguide material) or adjustment of the viscosity of the extruded
material or both, allowing the extruded material to sag somewhat
under its own weight. Thus, a substantial degree of control of both
wall angle and cross-sectional shape of the waveguide is provided
by the present invention.
In view of the foregoing, it is seen that the extrusion of
waveguides directly onto a surface in accordance with the present
invention provides a simple and inexpensive alternative to the
formation of waveguides through spin processes with improved
performance and which can accommodate severe surface topology. Any
of a number of waveguide shapes, profiles and cross-sections and
claddings and protective coverings can be formed by variations of
the invention involving only choice of materials and substitution
of nozzle structures. No changes in design, materials or structure
of electronic modules is required by the practice of the invention
and waveguides may even be retrofit onto existing modules in
accordance with the present invention.
While the invention has been described in terms of a single
preferred embodiment, those skilled in the art will recognize that
the invention can be practiced with modification within the spirit
and scope of the appended claims.
* * * * *